Recent attention has focused on carbon micro-electro-mechanical-systems (C-MEMS). Yet, microfabrication of C-MEMS carbon structures using current processing technology, including focus ion beam (FIB) and reactive ion etching (RIE), tends to be time consuming and expensive. Low feature resolution, and poor repeatability of the carbon composition as well as the widely varying properties of the resulting devices limits the application of screen printing of commercial carbon inks for C-MEMS. One promising C-MEMS microfabrication technique, however, is based on the pyrolysis of photo patterned resists (photoresists) at different temperatures and different ambient atmospheres. The advantage of using photoresists as the starting material for the microfabrication of various carbon structures is that the photoresists can be very finely patterned by photolithography techniques and hence a wide variety of repeatable shapes are possible. Moreover different temperature treatments result in different resistivities and mechanical properties. Some important C-MEMS properties includes: the material has a very wide electrochemical stability window, it exhibits excellent biocompatibility, is low cost, is very reproducible, very fine geometries can be defined as opposed to the more traditionally used printing of carbon inks, a wide range of resistivities and mechanical properties can be obtained, and the surface of this very chemically inert material is easy to derivatize. The material has particular importance in bioMEMS applications including DNA arrays, glucose sensors, and micro batteries.
Most pyrolyzed photoresist structures described in the literature today concern carbon features derived from positive photoresist and are very low aspect ratio. The fabrication of high aspect ratio and dense C-MEMS patterns is a challenging problem because with increasing photoresist thickness, the requirements of any lithography process increase exponentially. Basically, it is very difficult to design a thick positive tone photoresist chemistry to achieve the necessary transparency and to achieve reasonable exposure doses while maintaining excellent sidewall angles. The LIGA process in which PMMA resist is exposed with an x-ray source is capable of structures of the order of 1 mm. However, this technique requires an expensive synchrotron source, hence the motivation for cheaper and easier processes.
In many applications where the carbon micro-structures act as transfer interfaces, e.g., electrodes for battery applications, graft sites for DNA immobilization, sensing electrodes for chemical sensors, and the like, recent attention has focused on methods to improve surface-to-volume ratios and, thus, increase capacity per footprint, by increasing the surface area of the carbon micro-structures. Recent attention has also been focused on methods to provide structures that can act as bridges between micro-scale and nano-scale electronics.
Accordingly, it would be desirable to provide C-MEMS with carbon micro-structures having high surface areas and integrated structures that act as bridges between micro-scale and nano-scale electronics, and to provide improved methods for producing such structures.